Use of Edm and Proper Reduction of Observations

The standpoint is the station where the instrument is situated, and the forepoint is the point to which observations are being made (backsight or foresights). Figure 1, attached to this paper, shows the various distances discussed. They are described as follows: d1 is the wave path length (edm distance corrected for atmospheric delay), d2 is the wave path chord, d4 is the ellipsoidal arc length, and d3 is the ellipsoidal chord length. The horizontal chord length at the standpoint height is denoted d5. The mark-to-mark distance is dG. Because of the very small difference between the arc and chord distances, dedm will be used interchangeably with d1 and d2, and de with d3 and d4.